Field of the Invention
The present invention relates to a technique for detecting an abnormal state such as a scratch on a target object.
Description of the Related Art
A technique for detecting as a defect an abnormal state such as a scratch on the surface of a product or a component is termed defect inspection or abnormality detection and is widely known as a technique for use in automated manufacturing and inspection. The appearance of a scratch on the surface of a target object changes depending on the surrounding light source environment or the angle of observation. To that end, the manner of shedding light from a light source has been contrived, and a technique for further performing image processing to appropriately visualize an abnormal state such as a scratch has been discussed for a long time. The publication of Japanese Patent Application Laid-Open No. 2006-313146 discusses a method for using color light sources for coaxial epi-illumination and oblique incidence illumination to simultaneously inspect a depression/protrusion defect and a hue defect by capturing an image once. The publication of Japanese Patent Application Laid-Open No. 2009-097977 discusses a technique for using light sources already calibrated in at least four directions and a camera to determine whether a scratch portion is a protrusion or a depression. Further, the publication of Japanese Patent Application Laid-Open No. 2013-137239 discusses a method for comparing the results of measurements using light sources having three different types of wavelengths with master data to detect three states including a depression and a protrusion, a change in color tone, and a shine.
However, the technique in Japanese Patent Application Laid-Open No. 2006-313146 needs to calibrate the coaxial epi-illumination and the oblique incidence illumination, and the apparatus configuration is complicated. Further, the technique in Japanese Patent Application Laid-Open No. 2009-097977 cannot handle a defect and an abnormality other than a depression and a protrusion. Further, the technique in Japanese Patent Application Laid-Open No. 2013-137239 requires prior learning and a database such as master data and therefore cannot be applied to an unknown target object. Further, if a shadow falls on a target object, this technique may erroneously detect the shadow as a scratch.